Field of the Invention
The invention relates to a DMA or dynamic memory access control device for the transmission of data between a data transmitter and a data receiver via an external bus formed of a data bus, an address bus and a control bus to which a multiplicity of data transmitters/ receivers and at least one microprocessor are connected and in which the data are transmitted in dependence upon a channel program containing channel transfer commands and channel control commands.
From German Patent Nos. 23 39 813 and 23 39 787, it has become known that data transfers between a data transmitter, such as a memory, for example, and a data receiver, such as peripheral equipment, for example, are performed in a data processing system by means of so-called channel programs. The channel programs indicate how the data transfer should be performed; however, they also indicate how the organizational cycles, such as equipment start-up, interrogation of equipment state, equipment stop, and interrupt requests to the arithmetic unit etc. are to be carried out. The channel programs are performed in a data processing system of this type by means of channel mechanisms which perform the data transfer independently of the arithmetic unit of the data processing system.
The channel mechanisms of such large computers perform the data transfer either in selector operation or in multiplex operation. The multiplex operation may be byte multiplex operation or block multiplex operation. The transmission devices via which the data transfer is effected are hereinafter referred to as channels.
The data transfer between a data transmitter and the data receiver can also be controlled by means of microcomputer systems. Such microcomputer systems, as a rule, contain at least one microprocessor, a memory and peripheral equipment which are connected to an external bus either directly or via intermediate units. The addresses, the data and the control signals are then transferred via the external bus. The control of the data transfer, for example, between the memory and a peripheral equipment is controlled in dependence upon the afore-mentioned channel programs. For this purpose, the channel programs contain transfer commands which indicate from which data transmitter to which data receiver the data are to be transmitted, and control commands which control the organizational cycles.
In order to relieve the microprocessor of the control function it has become known heretofore to connect to the external bus additionally a DMA control device which controls the data transfer largely independently of the microprocessor. While the DAM control device carries out the data transfer, the microprocessor can take care of other problems. Such a microcomputer system is found, for example, in Elektronik-Praxis, No. 9, September 1982, pages 131 to 134.
An object of the invention is to provide a DMA control device which is constructed in MOS technology and affords data transmission at very high rates via one or more channels.